Diaphragm valves for fluid control have gases or liquids flow therethrough. In the case of three or more passageways opening into the valve chamber, individual passageways are separated from the remaining passageways, in order to realise for example a 3/2 way valve. Usually, a valve seat in the form of a web, in particular a linear web, is formed between directly adjacent passageway openings. A common diaphragm for a plurality of these valve seats is controlled in sections, so that the corresponding diaphragm section is deformed and is pushed against the valve seat correspondingly to be controlled or, vice versa, is released therefrom.
A generic diaphragm valve is shown in EP 0 705 403 B1. The three passageways are arranged next to each other, so that a central passageway can be flow connected with one of the two lateral passageways or, if the diaphragm is completely released from the valve seats, can be flow connected with both lateral passageways. The valve seats are disposed relatively close to each other, which makes the accommodation of the corresponding control pistons complicated. The control pistons, onto which pressure may be applied from opposite sides so as to move them into the opening and closing positions, require a certain minimum surface area, which is realised according to one embodiment by locating the control pistons on top of one another, i.e. in such a way that they are offset from one another. This means that the “upper” control piston has a ram that must penetrate through the lower control piston so as to be coupled to the diaphragm. In a second embodiment of this prior art document, the control pistons are not axially offset relative to each other in the actuating direction, i.e. if viewed in the axial direction, but rather the cylinder chambers are located at the same axial height, so that the control pistons can be moved next to each other. However, since the rams are disposed relatively close to the centroid of the control pistons, in order to avoid tilting movements, they are located relatively far away from each other and therefore have a relatively large lateral offset from the associated valve seats. This distance of the rams from the seats is disadvantageous for the actuation and above all for the sealing effect.
It is the object of the invention to improve a diaphragm valve in such a way that a reliable closing position can be achieved in the case of valve seats which are located relatively close to each other.